The invention relates to a device for inspecting the heat insulation of household appliances, more particularly refrigerators, such device being capable of detecting immediately and in a simple manner any deficiencies in the heat insulation during the manufacture of the appliances.
Nowadays, the mass production of a household appliance such as a refrigerator comprises the prefabrication of the body thereof in the form of a metal cabinet which is of substantially parallelepipedal shape and is open on its front side, and of a plastic cell of traditional type dimensioned to fit within such cabinet so as to define therewith an intervening space adapted to receive heat insulation.
The body, in turn, is provided with suitable fixtures for the attachment of a closure door on the front side of the cabinet, such door likewise being of parallelepipedal shape and comprising an outer metal covering and an inner door of plastic material, which elements can be fitted together so as to define an intermediate space adapted to receive heat insulation.
In practice, each door of the refrigerator is made separately from the corresponding body and each of these components is then transported separately by means known per se on a conveyor belt of an assembly line for carrying out processing steps adapted to produce, one after the other, the heat insulation of the body and of the door, as well as the assembling of the body with the door and with other operating components of the refrigerator.
In particular, this heat insulation is obtained by means of polyurethane materials which are known per se, and the liquid components of which are injected separately by traditional apparatus provided along the conveyor belt involved within the corresponding intermediate spaces in the body and the door, in which spaces such components polymerize (so-called foaming operation) and spread out in such a manner as to occupy all of such intermediate spaces.
In order to be able to carry out the foaming operations of the refrigerators satisfactorily, without defects being present in the heat insulation of such appliances, it is necessary that the equipment involved be caused to operate under the same operating and environmental conditions throughout the foaming operation and, furthermore, that the areas of injection of the bodies and doors of the respective refrigerators permit the effective penetration of the polyurethane material into the respective intermediate spaces of the bodies and doors.
In practice, however, such equipment is subject to operating and environmental conditions which at times vary during the foaming of the appliances in question, while the areas of injection of the polyurethane material themselves can, at times, have structural defects such as partly to prevent the penetration and proper distribution of the material throughout the above-described spaces.
Accordingly, under such conditions, defects may appear in the heat insulation of the refrigerators, due primarily to the presence of areas which are without polyurethane material (continuous and non-continuous holes) and areas in which such material is not completely polymerized (so-called "exhausted foam"), which defects result in a decrease of the insulating power of the layer of material and, in certain cases, even in the formation of heat bridges which significantly impair the functionality of the product.
At the present time, the presence of any defects of this type in the heat insulation of refrigerators is detected by the workers during the manufacture of these appliances by means of a number of visual and manual inspections in the areas of the appliances themselves in which such defects are most likely to be located.
While, on the one hand, this type of inspection makes it possible to single out practically all appliances that have defects located in areas which are directly noticeable from the outside, so that it is possible to discard such defective appliances or to perform operations thereon aimed at eliminating the defects found, this method is not, on the other hand, completely reliable in that it does not enable one to accurately examine the entire structure of the heat insulation and thus to single out any defective areas which are found in the insulation itself or which are difficult to locate by the inspections indicated above.